Composition of rail structure for supporting shadow mask in color CRT

ABSTRACT

Composition of a rail structure that can cut down cost of alloy composition, and enhance strength of the rail structure to minimize defects occurred in a fabrication process of the CRT, consisting of Fe as a main constituent, 22˜27 wt % of Cr, C≦0.02 wt %, Si≦0.40 wt %, Mn≦0.40 wt %, and P≦0.02 wt %, with addition of Mn as required.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a rail structure for supportinga shadow mask in a color cathode ray tube(CRT), and more particularly,to alloy composition of a rail structure that can cut down cost of alloycomposition, and enhance strength of the rail structure to minimizedefects occurred in a fabrication process of the CRT.

[0003] 2. Background of the Related Art

[0004] Referring to FIG. 1, a related art flat color CRT is providedwith a panel 3 of explosion proof glass 2, a funnel 4 sealed to thepanel, an electron gun 7 sealed in the funnel 4 for emitting red, green,and blue electron beams 6 toward the panel 3, and a fluorescent film 1of red, green, and blue color fluorescent materials coated on an insidesurface of the panel 3 for emitting lights of respective colors inresponse to the electron beams 6. The panel 3 is provided with a railstructure 9 for maintaining a fixed gap between the inside surface ofthe panel 3 and a shadow mask 8 having countless slots formed therein.As shown in FIG. 2, the rail structure 9 is welded on the panel 3 withthe frit 11 for enduring a tension from the shadow mask 8. The relatedart flat color CRT is further provided with a magnetic shield 10 forprotecting the electron beams traveling toward the fluorescent film froman external magnetic field.

[0005] When a power is applied to the CRT, the electron beams 6 areemitted from the electron gun 7 sealed in a neck part of the funnel 4,accelerated and converged as the electron beams 6 pass a plurality ofelectrodes in succession, selected of colors as the electron beams 6pass through the slots in the shadow mask 8, and hit the fluorescentfilm 1 coated on the inside surface of the panel 3, to reproduce apicture.

[0006] Referring to FIG. 3, the rail structure 9 has two long side rails9 a, two short side rails 9 b, and four end caps 9 c, welded together toform a rectangular structure. As shown in FIG. 2, Frit glass, a mixtureof Frit powder and vehicle, is filled in an empty space of therectangular rail structure, and melted in a furnace to fuse with thepanel 3. Top surface of the rail structure 9 is ground for providing thefixed gap between the panel 3 and the shadow mask 8. After thefluorescent material is coated on the panel with the rail structurefused thereon, the shadow mask is subjected to a tension, and welded onthe rail structure on an accurate position of the rail structure. Then,the panel 3 and the funnel 4 joined, and the electron gun 7 is inserted,and the completed CRT is evacuated.

[0007] In general, the rail structure 9 has compositions of 28˜29 wt %of Cr. and balance of Fe. As Cr costs approx. 7˜8 times higher than Fe,Cr is a cost raising element and is a cause of poor grinding due to thetoughness of the Cr. Moreover, as Cr forms Cr oxide during refiningprocess in a Cr steel production, high Cr steel has difficulty infabrication process, poor in acid cleaning after rolling, and liable todeformation during fabrication of the CRT owing to a low hardness.

SUMMARY OF THE INVENTION

[0008] Accordingly, the present invention is directed to composition ofa rail structure that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

[0009] An object of the present invention is to provide composition of arail structure, which can cut down a production cost, prevent productionof unnecessary oxide to improve mechanical properties, for preventingdeformation of rail during fabrication coming from a low hardness.

[0010] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings. Toachieve these and other advantages and in accordance with the purpose ofthe present invention, as embodied and broadly described, thecomposition of a rail structure consisting of Fe as a main constituent,22˜27 wt % of Cr, and inevitable impurities.

[0011] 1˜3 wt % of Mo is added thereto.

[0012] The inevitable impurities include C≦0.02 wt %, Si≦0.40 wt %,Mn≦0.40 wt %, and P≦0.02 wt %.

[0013] The composition consists of Fe as a main constituent, 25≦27 wt %of Cr, 1˜3 wt % of Mo, Ni≦0.5 wt %, Ti≦0.2 wt %, and the inevitableimpurities including C≦0.02 wt %, Si≦0.40 wt %, Mn≦0.40 wt %, and P≦0.02wt %.

[0014] The composition consists of Fe as a main constituent, 22˜24 wt %of Cr, 1˜3 wt % of Mo, Ni≦0.25 wt %, Ti≦0.3 wt %, and the inevitableimpurities including C≦0.02 wt %, Si≦0.40 wt %, Mn≦0.40 wt %, and P≦0.02wt %.

[0015] Thus, though the related art composition of a rail structurecosts high owing to use of more than 28 wt % of expensive Cr, but withinadequate tensile strength and hardness despite of a high content ofCr, the present invention provides a composition of a rail structureconsisting of a reduced content of Cr less than 27 wt %, and appropriateamount of elements, such as Mo and the like, thereby cutting down aproduction cost, preventing production of unnecessary oxides acting asforeign matter caused by oxidation of the rail structure during heattreatment of the CRT, and preventing deformation of the rail structureby improving mechanical properties thereof.

[0016] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciples of the invention:

[0018] In the drawings:

[0019]FIG. 1 illustrates a section of a color CRT;

[0020]FIG. 2 illustrates a process for fixing a rail to a panel,schematically; and, FIG. 3 illustrates a perspective view of a railfixed to a panel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings. After rail is formed of an alloy with chemicalcomposition as shown in the following table 1, the alloy is heated up,kept at an elevated temperature ranging 580˜1,150° C. for 1˜30 min.,cooled down, and mechanical properties thereof are tested. TABLE 1 unit:weight % C Si Mn P Ni Ti Mo Cr Fe *1 1 0.02 0.40 0.55 0.011 0.35 0.5019-21 Balance 2 0.06 0.39 0.36 0.016 0.23 0.23 0.30 19-21 Balance 3 0.020.39 0.36 0.016 0.23 0.30 0.30 19-21 Balance 2* 1 ≦0.02 ≦0.40 ≦0.40≦0.02 ≦0.25 ≦0.20 1.5-2.5 22-24 Balance 2 ≦0.02 ≦0.40 ≦0.40 ≦0.04 ≦0.50≦0.20 1.0-3.0 25-27 Balance

[0022] TABLE 2 Comparative The present inventions invention Tube size(1,2,3) 1 2 15″˜17″  0 0 0 19″ 50 0 0 21″ and over 50 7 0

[0023] TABLE 3 Y.S (kg/mm²) Hardness (HrB) 20% Cr steel 33.46 83.2Comparative inventions 26% Cr steel 41.18 89.5 The present invention 28%Cr steel 37.70 85.8 The related art

Comparative Invention 1

[0024] Hardness of the alloy of the comparative invention 1 is measuredto obtain HrB 110-15, which drops at a heat treatment temperature higherthan 950° C., to cause deformation of the rail structure duringfabrication of the CRT. Since a heat expansion coefficient of the alloyis in a range of 11.5E-6, approx. 9.5% higher than glass with a heatexpansion coefficient of 10.5E-6 at 30-400° C., that allows applicationto a 17″ size CRT, application of the alloy to a CRT with a size greaterthan 17″ has difficulty owing to frequent occurrence of cracks duringfabrication.

Comparative Inventions 2, and 3

[0025] Hardness of the alloys of the comparative inventions 1, and 2 aremeasured to obtain HrB 110-40. Since a heat expansion coefficients ofthe alloys are in a range of 11.3E-6 at 30-300° C., approx. 7.6% higherthan glass with a heat expansion coefficient of 10.5E-6 at 30-400° C.,that allows application to a color CRT, because application of thealloys to a CRT with a size 21″ and over causes cracks in a range of 50%under fabrication conditions identical to the related art shown in table2, while application of the alloys to a CRT with a size in a range of15″-17″ causes no cracks under fabrication conditions identical to therelated art as shown in table 2, the alloys can be applicable to alimited products with a size of 15″-17″.

Embodiment 1

[0026] Hardness of the alloy of the embodiment 1 is measured to obtainHrB 88-102, which is a value applicable to fabrication of the CRTwithout problem. Since a heat expansion coefficient of the alloy is in arange of 11.2E -6 at 30-300° C., approx. 6.7% higher than glass with aheat expansion coefficient of 10.5E-6 at 30-400° C., that allowsapplication to a color CRT, because application of the alloys to a CRTwith a size 21″ and over causes cracks in a range of 7% underfabrication conditions identical to the related art shown in table 2,while application of the alloys to a CRT with a size in a range of15″-19″ causes no cracks under fabrication conditions identical to therelated art as shown in table 2, the alloys can be applicable to alimited products with a size of 15″-19″.

Embodiment 2

[0027] Hardness of the alloy of the embodiment 2 is measured to obtainHrB 88-105, which is a value applicable to fabrication of the CRTwithout problem. Since a heat expansion coefficient of the alloy is in arange of 11.0E -6 at 30-300° C., approx. 4.8% higher than glass with aheat expansion coefficient of 10.5E-6 at 30-400° C., so as not to causecracks for entire models of color CRTs as shown in table 2, the alloyscan be applicable to all sizes of products.

[0028] Thus, the comparative inventions and the embodiments of thepresent invention are applicable, as the application is limited by sizesof the CRTs, an alloy of the second embodiment of the present inventionwith Cr 25˜27%, and Mo 2% is preferably the most applicable.

[0029] As has been explained, the present invention saves a productioncost by forming a rail structure for supporting a shadow mask, of analloy with low cost elements, enhances yield by dropping a chromecontent, and minimizes defects occurred in a fabrication of CRT byenhancing mechanical properties of the shadow mask supporting structure.

[0030] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the alloy composition of arail structure of the present invention without departing from thespirit or scope of the invention. Thus, it is intended that the presentinvention cover the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A composition of a rail structure consisting ofFe as a main constituent, 22˜27 wt % of Cr, and inevitable impurities.2. A composition as claimed in claim 1 , wherein the compositionconsists of Fe as a main constituent, 22˜27 wt % of Cr, 1˜3 wt % of Mo,and inevitable impurities.
 3. A composition as claimed in claim 1 or 2 ,wherein the inevitable impurities include C≦0.02 wt %, Si≦0.40 wt %,Mn≦0.40 wt %, and P≦0.02 wt %.
 4. A composition as claimed in claim 1 ,wherein the composition consists of Fe as a main constituent, 25˜27 wt %of Cr, 1˜3 wt % of Mo, Ni≦0.5 wt %, Ti≦0.2 wt %, and the inevitableimpurities including C≦0.02 wt %, Si≦0.40 wt %, Mn≦0.40 wt %, and P≦0.02wt %.
 5. A composition as claimed in claim 1 , wherein the compositionconsists of Fe as a main constituent, 22˜24 wt % of Cr, 1˜3 wt % of Mo,Ni≦0.25 wt %, Ti≦0.3 wt %, and the inevitable impurities includingC≦0.02 wt %, Si≦0.40 wt %, Mn≦0.40 wt %, and P≦0.02 wt %.